The present invention relates primarily to head transducer moving storage devices which, besides "Winchester" type devices, also include similar applications such as floppy disk which may also utilize the Bernoulli concept. The head transducer may be magnetic and/or optical in nature. If optical, the transducer may include invisible wavelength transducing or similar means, but is not limited thereto. The transducer interface may include a substantially fixed distance through the use of flying, viscous and/or contact means.
A large amount of disclosure relating to this invention particularly regarding the pivot technology including inherent partial rotation YAW-AXIS means is referred to in U.S. Pat. No. 4,995,025 Schulze.
Besides a customary spindle as a full turn mover, typically full-turn ball bearings are also used for linear slides and/or rotary pivot means suspending one or more heads and partial turn mover means like voice coils or magnets. Besides being costly, full turn ball bearing pivots also exhibit an undesirable amount of non-repeatable friction.
Ball bearing pivots also require tight tolerances for the interfacing parts. The seating, run-out and evenly distributed preload of the races are of great significance in order to assure proper servo-operation. Essentially two full turn ball bearings with several individual balls are required.
Each ball has at least two contact surfaces and even more when the balls either touch each other or a spacer cage.
In a certain scenario including droppage of a unit, two balls may encounter almost all of the Hertzian or surface stress on at least two convex surfaces, one being the ball and the other the circumference of the inner race, establishing unfavorable stress conditions and also allowing only relatively low stiffness.
The instant invention, by contrast, has substantially at least one but typically two contact areas for each of the two individual pin/cup means if sliding for repeatability is employed.
A convex and a concave interface, but not limited thereto, for lowering of surface tensions or stresses is utilized.
Optionally, the contact areas may be elongated in a direction along the pivot axis.
For typically round recording features like in Optical Recording with only a requirement for having to repeat perhaps a center position, only substantially one contact point per individual pin structure may be required. This rolling motion may also potentially yield the lowest amount of friction. In the abovementioned sliding motion with highest position repeatability requirements due to the elongate shape and accordingly tight skew requirements of the recording features, only typically two contact points/lines with only minute friction torque radii may generate perhaps a slightly higher amount of friction compared to rolling motion. In the context of this invention, these two contact points/lines per individual pin/cup shall be termed as one contact point. However, for full turn ball bearings, several balls are being used. First, the balls generate a sliding friction torque about their own radii when perhaps most contact each other or a spacer cage. Second, additional friction torque is generated by a much larger radius from the center of the bearing to the center of the individual balls including rolling motion and translated sliding motion. Besides other aspects, the friction torque for full turn ball bearings is typically higher. Depending on preload alignment of those ball bearings and/or head pair preload difference, the individual balls may aggregate on one side and generate a torque of a magnitude which voice coils particularly of smaller drives could not overcome. Especially here, distinction is also made between static and dynamic friction. In perspective, radii for the instant invention could progress down to about a thousands of an inch, but not limited thereto, while such functional radii for full turn ball bearings could be about several orders of magnitude higher. It is also shown that contactless magnetic preloading is very repeatable and can also accommodate for bias torques if needed. In ball bearings, by contrast, the balls can move around versus their original position and may or may not make contact in certain circumstances including reversal of direction besides others, generating non-repeatable friction. A high amount of friction also increases the dead-band. In the presence of an undesirably large dead-band, a higher amount of voice coil power has to be applied to overcome such friction before movement of the arm structure can occur. A low dead-band facilitates higher precision of the servo-operation.
The state of the art with full turn ball bearing pivots employs plane versus projected sheet-metal of the instant invention and also has a pivot housing as an integral portion of the deck means. However, such integral portion does not provide ferro-magnetic loop means as the instant invention may provide.